1. Field of the Invention
The present invention relates to radio communication devices constituting a system that forms a network in which a radio communication device operating as master terminal is connected to a plurality of radio communication devices operating as slave terminals using a short range radio communication function, and more specifically relates to radio communication devices in a radio communication system using these devices and method in which, when the master terminal or a slave terminal is disconnected from the network, the network is reconstructed with the same terminals, whereby short range radio communication can be performed favorably.
2. Description of the Related Art
Networks such as the Internet or Intranet, which transmit and receive data among information processing terminals such as personal computers or PDAs (Personal Digital Assistants), are constructed and used in various situations.
Networks are also often constructed using radio communication methods such as IrDA (Infrared Data Association) or Bluetooth (R) provided in communication terminals such as cellular phones, PDAs, and notebook computers.
Particularly in recent years, radio communication devices, which have a short range radio communication function such as Bluetooth and are capable of real time bidirectional communication among a plurality of terminals having the same function without passing through a server (online chat, for example), have been put to practical use.
In performing real time communication among a plurality of radio communication devices of this type, function setting is normally performed in one terminal in order for this terminal to operate as master terminal (master), and function setting is performed in the other terminals in order for these terminals to operate as slave terminals (slaves). The terminal set as master terminal then performs short range radio communication with the terminals set as slave terminals to thereby accommodate the slave terminals in a network with a star connection configuration.
As a specific example operating as a radio network constructed using Bluetooth, FIG. 1(a) shows a Piconet that performs two-way data communication in which one radio communication device (master terminal) 10-1 is connected one-to-one (point-to-point connection) with each of a plurality of radio communication devices (slave terminals) 10-2, 10-3, 10-4.
In the Piconet, once a radio communication device is initially designated as master terminal, it operates consistently as master terminal and performs control of the network until the network is abandoned.
Therefore, when online chat is performed by means of a radio connection among a plurality of cellular phones using Bluetooth, for example, the cellular phone which initially commences connection becomes the master terminal, and that terminal operates as master terminal until the chat session ends.
However, since the Piconet is a network in which the master terminal and the other terminals (slave terminals) are connected in point-to-point connection around the terminal initially designated as master terminal, the slave terminals only require control to perform point-to-point communication with the master terminal, whereas the master terminal requires multi-point connection control with the plurality of slave terminals. As a result, the communication load on the master terminal is extremely large and power consumption in the master terminal is much greater than in the other terminals.
Under this situation, battery power consumption in the master terminal becomes far greater than in the slave terminals, and hence the network cannot be maintained for a long period of time.
In order to solve this problem, a communication system is disclosed in Japanese Patent Application Laid-Open No. 2001-103570 (Japanese Patent Application H11-280649) in which the terminal set as master terminal receives battery information (remaining battery power and the like) from each of the terminals on the network which are set as slave terminals and from this battery information determines a terminal which is, to become the next master terminal. Then, when the conditions for master terminal/slave terminal switching are established, a master terminal/slave terminal switching command is transmitted to the terminal which is to become the next master terminal and thus the roles of master terminal and slave terminal are switched between terminals.
In this conventional system, however, upon determination of the terminal which is to become the next master terminal, the position of this terminal is not taken into account.
As a result, when the terminal with the largest remaining battery power is determined as the next master terminal (the terminal subject to switching), for example, the terminals forming the current network may not be included within the communication range of the terminal subject to switching.
In that event, in the network formed with the terminal subject to switching as the new master terminal, some terminals may come to fall outside of the communication range of the new master terminal, and thus communication cannot be performed among the same terminals as those in the network prior to switching.
As described above, as a method for dispersing the load on the master terminal to enable the construction of a long-term network, there was a method of having a master terminal determine the terminal with the greatest remaining battery power from among the terminals in a network as the terminal subject to switching and reconstructing the network with this terminal subject to switching as the new master terminal. In this method, however, a network which includes all of the terminals forming the current network cannot be reconstructed due to the positional relationship between the terminal subject to switching and the other terminals, and thus a problem arises in that short range radio communication among the same terminals as those prior to switching may not be maintainable.
Moreover, in the conventional communication system, it was the master terminal that performs control to determine the terminal subject to switching and reconstruct the network with the terminal subject to switching as the new master terminal, by issuing a master terminal/slave terminal switching command to the terminal subject to switching which is to become the next master terminal.
However, since a short range radio communication function such as Bluetooth which is installed in this type of radio communication device has a short transmission range and low transmission output, the master terminal may easily become disconnected from the network when, for example, a user carrying the master terminal sends and receives messages while in motion.
If the master terminal becomes disconnected from the network for such a reason, problems arise in the conventional system in that the network reconstruction control performed mainly by the master terminal in the network becomes impossible and the network cannot be reconstructed among the remaining terminals. As a result, communication cannot be maintained.